Software configurable distributed antenna system and method for bandwidth compression and transport of signals in noncontiguous frequency blocks

ABSTRACT

A method for transporting communications signals includes receiving an analog IF signal at a first unit. The analog IF signal includes a first carrier having a first frequency and a first bandwidth and a second carrier having a second frequency different from the first frequency and a second bandwidth. The analog IF signal is converted to a digitally sampled IF signal having the first carrier located in a first Nyquist zone, the second carrier located in a second Nyquist zone, an image of the first carrier located in a third Nyquist zone, and an image of the second carrier located in the third Nyquist zone. The image of the first carrier and the image of the second carrier is transmitted from the first unit to a second unit, where the image of the first carrier and the image of the second carrier is then converted to the analog IF signal.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/686,036, filed Nov. 27, 2012; which claims priority to U.S.Provisional Patent Application No. 61/564,211, filed on Nov. 28, 2011.The disclosures of these applications are hereby incorporated byreference in their entirety for all purposes.

BACKGROUND OF THE INVENTION

Wireless communication systems employing Distributed Antenna Systems(DAS) are available. A DAS typically includes one or more host units,optical fiber cable or other suitable transport infrastructure, andmultiple remote antenna units. A radio base station is often employed atthe host unit location commonly known as a base station hotel, and theDAS provides a means for distribution of the base station's downlink anduplink signals among multiple remote antenna units. The DAS architecturewith routing of signals to and from remote antenna units can be eitherfixed or reconfigurable. Sometimes a bi-directional amplifier or RFrepeater is used instead of an on-site base station to feed downlinkover-the-air signals from a nearby base station to the DAS, and to feeduplink signals from the DAS over-the-air to a nearby base station.

A DAS is advantageous from a signal strength and throughput perspectivebecause its remote antenna units are physically close to wirelesssubscribers. The benefits of a DAS include reducing average downlinktransmit power and reducing average uplink transmit power, as well asenhancing quality of service and data throughput.

Despite the progress made in wireless communications systems, a needexists for improved methods and systems related to wirelesscommunications.

SUMMARY OF THE INVENTION

The present invention relates to transporting RF signals innoncontiguous frequency blocks within a DAS. More specifically, thepresent invention relates to a DAS for which the routing and splittingfunctions of downlink signals within the DAS and the routing andcombining functions of uplink signals within the DAS are reconfigurablebased on software configurable subsystems deployed at the host unit orhost units and/or at the remote antenna units.

A DAS includes one or more Digital Remote Units (DRUs) and one or moreDigital Access Units (DAUs). The DAU typically interfaces to a BaseStation and the DRU is remotely located in the desired coverage area.The DRU receives the uplink signals from the mobile terminals andtransports them to the DAU. The transport medium between the DAU and DRUmay be Optical Fiber, Coaxial Cable, twisted pair cable, Microwave Link,or other transport media. In order to efficiently transport RF signalsthat are not spaced compactly, i.e., immediately adjacent to one anotherin the frequency domain, signal processing techniques may be used toreduce the data rate associated with transport of the signals.

Some DAS applications involve the transport of multiple Wirelessoperator frequency bands over the transport medium. In the case of anoptical fiber transport medium, the transport data rate is a criticalparameter that affects the cost and performance of the system. Thetransport data rate is controlled by the operator's assigned RFbandwidth and dynamic range of the signals to be transported. In thecase of a Neutral Host DAS, the total RF bandwidth corresponds to thecombined RF bandwidth of multiple operators. DAS systems that transportmultiple operator bands will typically accommodate the aggregate RFbandwidth resulting from each operator's frequency bands.

Applications arise where the RF bandwidth may not be fully utilized andonly a few radio frequency carriers are positioned within the entirebandwidth. This system is classified as having signals in noncontiguousfrequency blocks. A conventional approach would be to transport theentire bandwidth from the DRU to the DAU. However, this would be a veryinefficient use of the optical transport data rate. A more efficientapproach would be to channelize or filter the active bandwidth segmentsand transport only the information carried in the active bandwidthsegments. Although this approach would reduce the effective opticaltransport data rate, the addition of the channelized filters increasesthe system delay and complexity.

Another approach to more efficiently transport the RF signals is byemploying digital signal processing. The RF bandwidth associated withthe RF signals is assumed to contain two or more carriers positionedwithin the RF bandwidth. The uplink RF signals at the DRU may betranslated to an IF frequency before they are fed into an Analog toDigital Converter (ADC). By properly selecting the sampling rate of theADC with respect to the IF frequency, the carriers' respective positionsare defined so that the resulting images fall within different Nyquistzones. This approach causes the respective carriers' images to fold intothe same Nyquist zone. The net effect is to transform the carriers innoncontiguous frequency blocks into a more compact bandwidth (i.e.,compressed bandwidth) for transport over the optical fiber. The overallresult is a significantly reduced optical transport data rate usage fortransporting these carriers, while maintaining the appropriate value ofdynamic range.

The bandwidth-compressed uplink signal is transported from the DRU toone or more DAUs. The DAU performs an inverse transformation in order toreconstruct the uplink signal including the individual carriers at theiroriginal locations within the original bandwidth of operation. The DAUthen feeds the uplink signals to the uplink port of the Base Station.

The bandwidth compression technique of the present invention can also beused for processing the downlink signal. Downlink refers to thetransport of the RF signal from the Base Station to the DAU, thenoptically transporting it to one or more DRUs.

Wireless and mobile network operators face the continuing challenge ofbuilding networks that effectively manages high data traffic growthrates. Wireless and mobile technology standards are evolving towardshigher bandwidth needed for high peak data rates and cell throughputgrowth.

Conventional radio base stations employed in wireless networks utilizevarious 2G, 2.5G, 3G and 4G radio technologies (such as CDMA, CDMA1xEV-DO, WCDMA, WiMAX, LTE, etc.).

The present invention substantially overcomes the limitations ofconventional DAS solutions employing transport technologies withbandwidth limitations. The bandwidth limitations seen with the transporttechnology typically result from transport data rate performancetradeoffs due to component and subsystem costs. Leading cost driversinclude optical transceivers and DSP processors. Accordingly, it is anobject of the present invention to provide a high performance,cost-effective, dynamically reconfigurable DAS system, architecture andmethod which offers a bandwidth compression technique for reducing theoptical data transport rate in the system.

Embodiments of the present invention employ a bandwidth compressiontechnique via signal processing to reduce the total bandwidth needed fortransporting carriers in noncontiguous frequency blocks. The techniqueuses the images that result from sampling the carriers when the carriersare placed in different Nyquist zones. The technique is applicable tosystems that utilize multiple carriers. This technique is alsoapplicable when some of the carriers reside in the same Nyquist zones.

This technique provides features to enhance the cost-effectiveness,flexibility and system performance for applications where multipleremote antenna units are deployed. Systems that are employed in thepresent invention, include one or more Digital Access Units (DAUs), aRemote Radio Head Unit (RRU), and/or one or more Digital Remote Units(DRUs).

The present disclosure describes embodiments to provide performanceenhancements for a DAS including one or more DAUs, optical fibertransport, and one or more RRUs.

The present invention relates to methods and systems that employ abandwidth compression technique via signal processing to reduce thetotal bandwidth needed for transporting carriers in noncontiguousfrequency blocks. In an embodiment, the technique uses the images thatresult from sampling the carriers when the carriers are placed indifferent Nyquist zones. The technique is applicable to systems thatutilize multiple carriers. This technique is also applicable when someof the carriers reside in the same Nyquist zones.

In some embodiments, a method is presented for transportingcommunications signals. The method may include receiving an analog IFsignal at a first unit, wherein the analog IF signal includes a firstcarrier having a first frequency and a first bandwidth and a secondcarrier having a second frequency different from the first frequency anda second bandwidth. A sampling signal having a sampling frequency may beprovided. The analog IF signal may then be converted to a digitallysampled IF signal, wherein the digitally sampled IF signal includes: thefirst carrier located in a first Nyquist zone, the second carrierlocated in a second Nyquist zone, an image of the first carrier locatedin a third Nyquist zone, and an image of the second carrier located inthe third Nyquist zone. The third Nyquist zone may be at a lowerfrequency bandwidth than the first and second Nyquist zones, and ingeneral the first, second, and third Nyquist zones may be in any orderof frequency bandwidths relative to each other. The image of the firstcarrier and the image of the second carrier may be transmitted from thefirst unit to a second unit. The image of the first carrier and theimage of the second carrier may be received at the second unit. A secondsampling signal have a second sampling frequency may then be provided,and the image of the first carrier and the image of the second carriermay be converted to the analog IF signal.

In some embodiments, the first unit comprises a DRU and the second unitcomprises a DAU. In some embodiments, the first unit comprises a DAU andthe second unit comprises a DRU. In some embodiments, the digitallysampled IF signal is filtered to remove unneeded samples and reflectionsof signals. In some embodiments, the step of transmitting the image fromthe first unit to a second unit may be performed using an Ethernetcable, an optical cable, a microwave link, a coaxial connection, or awireless link. In some embodiments, the step of transmitting the imagefrom the first unit to the second unit may be using a parallel connectorindependent of a SERDES.

In some embodiments, a system or apparatus may be presented, the systemor apparatus be operable to perform any of the methods described herein.The system or apparatus may include a first unit having an input port,and an A/D converter coupled to the input port. The system or apparatusmay include second unit including a D/A converter, and a transmissionlink coupling the first unit and the second unit, wherein thetransmission link. The input port, A/D converter, D/A converter andtransmission link may be operable to perform the steps of any of themethods described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects and advantages of the invention can be more fullyunderstood from the following detailed description taken in conjunctionwith the accompanying drawings.

FIG. 1 shows an example of a DAS architecture, highlighting theinterfaces between a Base Station (BTS), a Digital Access Unit (DAU) andmultiple Digital Remote Units (DRUs).

FIG. 2 illustrates the transport of a wireless uplink signal from theDRU to the base station. The wireless uplink signal is represented astwo carriers in noncontiguous frequency blocks.

FIG. 3 shows an embodiment illustrating the uplink signal bandwidthcompression technique of the present invention, which is employed withinthe DRU.

FIG. 4 shows an embodiment illustrating the reconstruction of the uplinksignal using the bandwidth decompression technique of the presentinvention, which is employed within the DAU.

FIG. 5 shows an embodiment illustrating the downlink signal bandwidthcompression technique of the present invention, which is employed withinthe DAU.

FIG. 6 shows an embodiment illustrating the reconstruction of thedownlink signal using the bandwidth decompression technique of thepresent invention, which is employed within the DRU.

FIG. 7 is a simplified schematic diagram illustrating a system includingbandwidth compression techniques provided by an embodiment of thepresent invention for an uplink signal comprising two wireless carrierswith wide frequency spacing.

FIG. 8 is a simplified flowchart illustrating a method of transmittingcommunications signals according to an embodiment of the presentinvention.

FIG. 9 is a simplified schematic diagram illustrating a system includingbandwidth compression techniques provided by an alternative embodimentof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

According to embodiments of the present invention, a novel DistributedAntenna System (DAS) that exploits the Software Configurable Radiosubsystem (referred to hereinafter as software defined radios or asoftware-defined digital platform) is provided. Embodiments enable DAUs,RRUs, and DRUs to communicate with each other.

Moreover, the system is flexible with regard to being able to supportvarious radio technologies, such as CDMA, CDMA 1xEV-DO, TD-SCDMA, WCDMAand LTE. However, embodiments may not be limited to these, as otherapplicable radio technologies may be apparent to those with ordinaryskill in the art.

FIG. 1 shows a block diagram of an exemplary Distributed Antenna System(DAS). Each DRU may receive wireless uplink signals 101, 104, or 106 atits antenna. The DRUs may each be connected to a DAU 103 via an opticalfiber 102, 105 or 107, and the DAU 103 may be connected to a BTS 108 viaone or more RF cables 109. The DRU may transport the uplink signals tothe DAU via the optical fibers. The DAU 103 may receive wirelessdownlink signals from the BTS 108. The DAU 103 may transport downlinksignals, not shown, to each of the DRUs via the optical fibers 102, 105,or 107. The DAU 103 and the DRUs may each contain a software-defineddigital platform.

Still referring to FIG. 1, DRU 1 receives wireless uplink signals 101,represents the signals 101 in a digital format and transports them viaoptical fiber 102 to DAU 103. Similarly, DRU 2 receives wireless uplinksignals 104, represents the signals 104 in a digital format andtransports them via optical fiber 105 to DAU 103. Similarly, DRU Nreceives wireless uplink signals 106, represents the signals in adigital format and transports them via optical fiber 107 to DAU 103. DAU103 processes all the incoming optical signals containing the respectiveuplink signals, according to the settings entered within thesoftware-defined digital platform within the DAU 103. DAU 103 thenconverts the appropriate uplink signals to RF and routes the appropriateRF uplink signals to BTS 108 via RF Cable 109.

An alternative embodiment may be described as follows. Instead offeeding one DRU with one optical fiber, the DRU may in turn feed asecond DRU in a daisy-chain configuration, meaning the DRUs may belinked in a sequence with each other, via optical fiber or similarcommunication means. An additional embodiment is one where multipleoptical fibers may be used to interconnect the DAU with a single DRU, inorder to deliver additional capacity to the DRU.

A further alternative embodiment may be described as follows. Instead ofhaving only one DAU in the system, two or more DAUs may be daisy-chainedor networked in order to provide a capability for digital combining ofsignals from multiple base stations which in turn feed the various DRUs.For this embodiment, the base stations may either be on differentfrequencies in different bands, on different frequencies within the sameband, or on the same frequencies in the same band. The latter embodimentrelates to an application for capacity enhancement at a specific DRUwhere it is advisable to avoid sharing of radio resources among multipleDRUs. In that case, multiple co-channel base stations would typically beconnected to the DAUs.

An alternative embodiment may be described as follows. Instead of usingan optical fiber link to transport signals from the DAU to DRU 1 as inFIG. 1, a point-to-point microwave link may be used for transporting thesignals in both directions. Also, instead of using an optical fiber linkto transport signals from the DAU to DRU 1, a wire cable such asunshielded twisted pair may be used for transporting the signals in bothdirections.

A further alternative embodiment may be described as follows. Instead ofusing an RF cable to connect signals between the BTS and DAU, an RFrepeater can be used to transport RF signals over-the-air between anearby base station site and the DAU.

Another alternative embodiment may be described as follows. Instead ofusing a DAU 103 to interact between DRUs and a BTS 108, each DRU may beconnected to the base station 108 without a DAU 103. This configurationmay be sometimes called a remote radio head, and the DRUs may be calledRRUs in this case. Persons skilled in the art would appreciate otherembodiments of the present invention based on similar DAS architecturesas described herein, either singly or in combination.

FIG. 2 illustrates the transport of a wireless uplink signal from theDRU to the base station. The wireless uplink signal is represented astwo carriers in noncontiguous frequency blocks. Referring to FIG. 2, DRU1 receives wireless uplink signals 201, represents the signals in adigital format and transports them via optical fiber 202 to DAU 203. DAU203 then converts the appropriate uplink signals to RF and routes theappropriate RF uplink signals to BTS 204.

An example of two carriers in noncontiguous frequency blocks is asfollows, with reference to FIG. 2. Carrier 1 may be a 5 MHz wide WCDMAcarrier, Carrier 2 may be a 5 MHz wide CDMA carrier and there may be a15 MHz wide gap between the 2 carriers, the total bandwidth occupied bythe two carriers and including the gap is 25 MHz. With regard to FIG. 2,the optical fiber transport function allocates at least 25 MHz to theuplink signal. It would be highly desirable to employ a bandwidthcompression technique to reduce the allocated bandwidth for the opticalfiber transport function.

FIG. 3 shows an embodiment illustrating the uplink signal bandwidthcompression technique of the present invention, which is employed withinthe DRU. Referring to FIG. 3, the uplink input signal 301 comprising twowireless carriers is frequency translated by RF Processing Function 302and IF Processing Function 303 to an Intermediate Frequency (IF). The IFsignal 304 is then sampled by ADC 305 at a rate which causes the imagesof the two uplink carriers to be positioned within separate Nyquistzones. In general a Nyquist zone as used herein may refer to thestandard definition of Nyquist zone as used and understood according tothose with ordinary skill in the art, e.g. each zone represents asampling of the signal in question where the sampling rate is no slowerthan 2B (the Nyquist rate), where B is the highest frequency of thesignal in question. As is seen in FIG. 3, the images fold into the sameNyquist zone so as to create a compact compressed bandwidth.

The Digital signal processing function 306 helps prepare the signals fortransport over the optical fiber. The Serializer/Deserializer (SERDES)307 translates the parallel bit streams into serial bit streams, and theresulting serial bit stream corresponding to signal 309 is fed to theOptical Transport function 308.

It is readily understood that although FIG. 3 describes the uplinksignal as comprising two carriers, various embodiments of the presentinvention may include two or more noncontiguous bandwidths.

FIG. 4 shows an embodiment illustrating the reconstruction of the uplinksignal using the bandwidth decompression technique of the presentinvention, which is employed within the DAU. The compressed bandwidth isreconstructed back to its original form and the resulting signal is fedinto the base station. Referring to FIG. 4, the serial bit stream 402 isfed from the Optical Transport function 401 into theSerializer/Deserializer (SERDES) 403 which translates the serial bitstream into parallel bit streams. The parallel bit streams are fed intothe Digital Signal Processing function 404 which prepares the signals tobe processed by DAC 405, which samples the resulting signal at a ratesuch that the signals are reconstructed and returned to theirappropriate positions in the IF domain (Signal 409) as seen in FIG. 4.The IF Processing function 406 and the RF Processing function 407translate the IF signal back to the RF domain, and the resulting signal410 is fed to the BTS 408.

FIG. 5 shows an embodiment illustrating the downlink signal bandwidthcompression technique of the present invention, which is employed withinthe DAU. The DAU contains the functions which process the downlinksignal in preparation for transport over the optical fiber to one ormore DRUs. Referring to FIG. 5, the downlink input signal 501 comprisingtwo wireless carriers is frequency translated by RF Processing Function502 and IF Processing Function 503 to an Intermediate Frequency (IF).The IF signal 504 is then sampled by ADC 505 at a rate which causes theimages of the two downlink carriers to be positioned within separateNyquist zones. As is seen in FIG. 5, the images fold into the sameNyquist zone so as to create a compact compressed bandwidth. The Digitalsignal processing function 506 helps prepare the signals for transportover the optical fiber. The Serializer/Deserializer (SERDES) 507translates the parallel bit streams into serial bit streams, and theresulting serial bit stream corresponding to Signal 509 is fed to theOptical Transport function 508.

It is readily understood that although FIG. 5 describes the downlinksignal as comprising two carriers, the embodiment would apply as well totwo or more noncontiguous bandwidths.

It is readily understood that although FIG. 5 may be discussed inreferences to the use of a single RF-to-IF frequency translator for bothof the two downlink carriers, embodiments would apply as well in theevent that multiple RF-to-IF frequency translators were used along withan IF summing function whose output feeds the ADC.

FIG. 6 shows an embodiment illustrating the reconstruction of thedownlink signal using the bandwidth decompression. Referring to FIG. 6,the serial bit stream 602 is fed from the Optical Transport function 601into the Serializer/Deserializer (SERDES) 603 which translates theserial bit stream into parallel bit streams. The parallel bit streamsare fed into the Digital Signal Processing function 604 which preparesthe signals to be processed by DAC 605, which samples the resultingsignal at a rate such that the signals are reconstructed and returned totheir appropriate positions in the IF domain (Signal 608) as seen inFIG. 6. The IF Processing function 606 and the RF Processing function607 translate the IF signal back to the RF domain, and the resulting RFsignal 609 is transmitted from the DRU.

FIG. 7 illustrates an embodiment wherein the bandwidth compressiontechnique of the present invention may be employed for an uplink signalcomprising two wireless carriers with wide frequency spacing BW_(i) 707.For illustration, the uplink signal 707 includes a Lower Band and anUpper Band. The uplink wireless signal is received at the DRU and thenfrequency translated down to a selected Intermediate Frequency (IF)which is referred to as F_(if). The IF signal 707 comprises two carriersin noncontiguous frequency blocks inside the total signal bandwidth. Insome cases, without employing embodiments of the invention, the signalwill have to be sampled at twice the bandwidth BW_(i) even though nosignal is being transported between the lower and upper bands. Thus,direct processing and transport of this signal without any bandwidthcompression through embodiments of the present invention would result inan inefficient utilization of the optical fiber transport data rate.After signal 707 is IF frequency translated, IF signal 707 is then fedinto ADC 706.

The inset 708 in FIG. 7, subtitled “DRU Signal Processing (After ADC),”illustrates an exemplary implementation for how embodiments of thepresent invention compress the received signal having bandwidth, BW_(i)707, into a compressed signal having compressed bandwidth BW_(c) 709. Byselecting the ADC sampling rate F_(S) with respect to the selected IFfrequency F_(if) such that the Lower and Upper bands appear in differentNyquist zones, images of the sampled carriers will be folded within thesame Nyquist zones. The 1st Nyquist zone 714 is from DC to ½ thesampling rate (F_(S/2)). The 2nd Nyquist zone 713 is from ½ the samplingrate (F_(S/2)) to the sampling rate (F_(S)). The 3rd Nyquist zone 712 isfrom the sampling rate (F_(S)) to 3/2 the sampling rate (3F_(S/2)).Higher Nyquist zones continue in this same fashion. Exemplaryembodiments of the invention involve selecting an appropriate samplingrate F_(S) such that the Lower band (LB) and Upper band (UB) of BW_(i)707 fall into two separate Nyquist zones. Once F_(S) is selected tosatisfy this condition, the translation of the original received signalinto an intermediate frequency F_(if) typically is chosen next, whereF_(if) is the frequency centered at the bandwidth BW_(i) 707,appropriately such that F_(if)<F_(S), and the choice of F_(if) stillallows the Upper and Lower bands to fall within separate Nyquist zonesbased on F_(S).

In the example shown in FIG. 7, the Lower band (LB) is shown to fallwithin the 2^(nd) Nyquist zone 713, which is designated as the bandwidthbetween half the sampling rate F_(S) to the sampling rate F_(S).Similarly, the Upper band (UB) is shown to fall within the 3^(rd)Nyquist zone 712, which is designated as the bandwidth between thesampling rate F_(S) and 3/2 of the sampling rate F_(S). The Upper bandand Lower band are placed in separate Nyquist zones, such thatF_(if)<F_(S). In other embodiments, the Upper and Lower bands may bereversed; that is, the Upper band may fall within the 2^(nd) Nyquistzone while the Lower band falls within the 3^(rd) Nyquist zone. In otherembodiments, the Upper and Lower bands may be in a different orderedsequence of Nyquist zones, e.g. Upper and Lower bands fall within the4^(th) and 5^(th) Nyquist zones, or 1^(st) and 2^(nd) Nyquist zones,etc. As an example, FIG. 9 provides additional description ofalternative embodiments.

The images of the carriers before sampling each appear in differentNyquist zones and through the sampling process of the ADC 706 the imagesare then folded into the same Nyquist zone in order to result in acompact spectrum for the combined carriers. This folding of carriersinto the same Nyquist zone is an inherent bi-product of selecting F_(S)and F_(if) such that the Upper and Lower bands fall within separateNyquist zones. The images of each of the Upper and Lower bands areinherently reflected into the other multiple Nyquist zones (e.g. UB′ andLB′, respectively), as shown in the inset 708 of FIG. 7, resulting inboth Upper and Lower bands appearing in the same Nyquist zone, e.g. the1^(st) Nyquist zone 714 and the 4^(th) Nyquist zone 711, but atcompressed bandwidths BW_(c).

Thus, in certain embodiments of the invention, the choice of samplingrate F_(S) with respect to IF frequency F_(if) is made so that thecarriers are closely spaced and yet can easily be reconstructed so thatthey are repositioned at the original frequency spacing without a highcomplexity of digital signal processing. In some embodiments, F_(S) andF_(if) are selected with an added condition that the resultingcompressed signal does not place both Upper and Lower bands so closetogether that it becomes difficult to filter the two signals and alsoreconstruct the original signal. In some embodiments, the particularchoice of sampling rate F_(S) and IF frequency F_(if) may depend on thebandwidth of the signals to be compressed and should be selected basedon employing practical filtering to reconstruct the signals with theiroriginal frequency spacing. The selection of the most appropriateNyquist zone to use in processing the carriers' images is driven by thefact that the signal-to-noise ratio is degraded at the higher Nyquistzones. Namely, exemplary embodiments select the 1^(st) Nyquist zone 714to process the compressed signal having bandwidth BW_(c), because the1^(st) Nyquist zone 714 has a better signal-to-noise ratio than thehigher Nyquist zones.

The resulting signal 708 comprising the compressed bandwidth carriers isthen further translated in the Digital Down Converter (DDC) anddecimator 705 so that the resultant signal 709 is at baseband and isformatted as parallel bit streams. This means that typically, thesignals falling within the higher Nyquist zones, e.g. 2^(nd) Nyquistzone 713, 3^(rd) Nyquist zone 712, 4^(th) Nyquist zone 711, etc., arefiltered out, such that only the compressed signal 708 remains. Noticethat while the original signal placed in the 2^(nd) and 3^(rd) Nyquistzones are filtered out, no information is lost with respect to theoriginal signal, since both Upper and Lower bands are inherentlyreplicated into the 1^(st) Nyquist zone 714.

Alternative embodiments of the present invention may switch the order ofwhether F_(S) or F_(if) is chosen first, relative to the other parameterand subject to the above mentioned constraints. In other embodiments,F_(S) or F_(if) may be fixed, while the other parameter is chosenrelative to the fixed parameter and subject to the above mentionedconstraints.

As will be discussed below, the translation to baseband in the DRU isnot necessarily limited to employing a Digital Down Converter (DDC) anddecimator. Other embodiments may involve different filtering means thatwould be readily apparent to those with skill in the art. The basebandsignal has a compressed bandwidth BW_(c) 709, which means that a lowerdata rate can be employed to preserve all the information contained inthe two carriers, which is a key advantage of embodiments of the presentinvention. The baseband signal 709 is then delivered to the SERDES 704for transport over the optical fiber 703.

The optical data at the end of the optical link 703 is then delivered tothe SERDES 702 in the DAU. At the DAU the signal output from the SERDESis then Digitally Up Converted (DUC), Filtered and then DigitallyDownconverted (DDC), in 701, so as to reconstruct the original signal atdigital IF. The reconstruction at the DAU from the baseband signal to anIF signal is not limited to DUC-Filter-DDC processes. The carriersreceived from SERDES 702 are individually filtered and translated to theoriginal frequency spacing as in 707.

The reconstructed digital IF signal is then fed into the Digital toAnalog Converter (DAC) 700 and the DAC output will be an analog IFsignal 710 with the same carrier spacing as the DRU input IF signal 707.

As mentioned previously with regard to FIG. 7, the translation tobaseband in the DRU is not necessarily limited to employing a DigitalDown Converter (DDC) and decimator. An alternative embodiment wouldemploy independently processing the individual carriers and combiningthem at baseband.

An alternative method for processing the uplink signal in the DRU tocompress the bandwidth would be as follows. A quadrature modulator canbe utilized for translating the IF signal 707 directly to baseband usingin-phase and quadrature (I and Q) representations of the uplink signals,which are then fed into dual ADCs. The respective outputs of the ADCsare then digitally processed so as to compress the overall bandwidth ofthe combined signals. Frequency translation of the individual carriersfollowed by filtering can be used to result in a bandwidth-compressedsignal as in 709.

An alternative embodiment would be to choose a different IF frequency atthe DRU then the one at the DAU. If the sampling rate is common betweenthe DAU and DRU, then the IF frequency at the DRU can be chosenindependently form the IF frequency at the DAU. The signal processing atthe DRU and DAU will ensure that the signals are translated correctlybetween units.

An alternative embodiment would be to choose a different Samplingfrequency at the DRU then the one at the DAU. If the IF frequency iscommon between the DAU and DRU, then the Sampling frequency at the DRUcan be chosen independently form the Sampling frequency at the DAU. Thesignal processing at the DRU and DAU will insure that the signals aretranslated correctly between units.

FIG. 7 depicts the transportation of the Uplink signal from the DRU tothe DAU. An analogous process is used to transport the downlink signalfrom the DAU to the DRU. A difference is that signal 707 will appear atthe input to the DAU and signal 710 will appear at the output from theDRU.

Advantages of embodiments of the present invention may include moreefficient implementation of wireless communications systems. Forexample, for a given cell phone of a user, there may be a number ofbands at which the cell phone operates. The cell phone may operate atvarying megahertz frequencies, e.g. 1900 MHz, 850 MHz and 700 MHz. Acell phone provider, e.g. Verizon® or AT&T®, may need to be able tohandle all these bands in order to cover all modes of communication ofthe cell phone. However, for example, in the 700 MHz band Verizon® andAT&T® own spectrum, the spectrums are actually quite a ways apart, e.g.about 150 MHz between each spectrum of Verizon® and AT&T®. Withembodiments of the present invention, implementations use only fourbands, whereas conventional products would utilize five bands. Thus,whereas a conventional product may have to utilize a separate band for afirst operator and a separate band for a second operator, the bandwidthcompression techniques described herein can combine the traffic from themultiple operators into a single band.

FIG. 8 is a simplified flowchart illustrating a method of transportingcommunications signals according to an embodiment of the presentinvention. The exemplary method starts at block 810, wherein a firstunit, e.g. a DRU, may receive signals with noncontiguous frequencyblocks, e.g. two carriers, a lower band and an upper band, spanningtotal bandwidth BW_(i) between them. The signals may be analog ordigital signals. The signals may be then translated into intermediatefrequency (IF) signals, as shown in block 812. Translating the originalsignals into IF signals enables embodiments of the present invention tomore easily manipulate the signals using signal processing devices knownin the art.

The method continues to block 814, where signal compression techniquesof the present invention may compress the bandwidth BW_(i) between thelower band and upper bands into a compressed bandwidth BW_(c). Exemplarycompression techniques of the present invention are described in FIG. 7,above. Block 814 may include other signal processing techniques, forexample the use of an ADC module if the original signals were analogsignals.

In some embodiments, in between blocks 814 and 816, the signalsprocessed through the compression technique may also be filtered, suchthat only the compressed signals remain. This may be done throughvarious means, such as a DDC and a decimator, or other filtering meansthat would be apparent to those with skill in the art. The compressedsignals may then be converted into their in-phase (I) andquadrature-phase (Q) components, and may also be downconverted. The Iand Q components of the compressed signals may then be processed througha Serializer/Deserializer (SERDES), in anticipation of being transmittedthrough a transmission link.

At block 816, the compressed signals may then be transmitted across atransmission link to a receiver of a second unit. The transmission linkmay be an optical link transmission, Ethernet cable, Microwave Link,coaxial connection, Wireless link, or other transmission means forcarrying a signal to a second unit. The second unit may be a DAU, or inother embodiments may be the base station itself.

At block 818, the second unit, e.g. DAU, receives the compressed signalsvia the transmission link. If the signals were converted into their Iand Q components, and/or were processed through a SERDES, then thecompressed signals would need to be inverse-processed using anotherSERDES, digital down-converter (DDC), digital up-converter (DUC),various filters or other means known in the art.

Finally, at block 820, reconstruction techniques are employed thatreverse the bandwidth compression of the IF signals, wherein none of theinformation of the original signals is lost. The signals may passthrough a DAC if the original signals were analog signals, and beutilized by the second unit or passed on to another unit, e.g. a basestation, for information processing or the like. It is apparent by thismethod that embodiments of the present invention may be viewed as“symmetric,” in that the processing conducted on either end of themethods described a reversed with no loss of information. Therefore, itis apparent that the techniques described herein can be reversed, inthat the same bandwidth compression and decompression techniques can beemployed starting from the second unit, e.g. the DAU or base station,and ending at the first unit, e.g. the DRU. These techniques may beconsistent with those described in any and all of FIGS. 1 through 7.

It should be appreciated that the specific steps illustrated in FIG. 8provide a particular method of transporting communications signalsaccording to an embodiment of the present invention. Other sequences ofsteps may also be performed according to alternative embodiments. Forexample, alternative embodiments of the present invention may performthe steps outlined above in a different order. Moreover, the individualsteps illustrated in FIG. 8 may include multiple sub-steps that may beperformed in various sequences as appropriate to the individual step.Furthermore, additional steps may be added or removed depending on theparticular applications. One of ordinary skill in the art wouldrecognize many variations, modifications, and alternatives.

FIG. 9 illustrates an alternative embodiment wherein the bandwidthcompression technique of the present invention may be employed for anuplink signal comprising two wireless carriers with wide frequencyspacing BW_(i) 907. The uplink signal 907 includes a Lower Band and aUpper Band. The uplink wireless signal is received at the DRU and thenfrequency translated down to a selected Intermediate Frequency (IF)which is referred to as F_(if). The IF signal 907 comprises two carriersin noncontiguous frequency blocks inside the total signal bandwidth.Direct processing and transport of this signal without any bandwidthcompression would result in an inefficient utilization of the opticalfiber transport data rate. IF signal 907 is fed into ADC 906. For thisembodiment the first carrier is positioned inside the 1^(st) Nyquistzone and the second carrier is positioned inside the 2^(nd) Nyquistzone. The image of the second carrier (i.e., upper band) is positionedin the 1^(st) Nyquist zone within the bandwidth BW_(i) of the firstcarrier (i.e., the lower band). Thus, this alternative embodimentdiffers from the embodiment illustrated in FIG. 7, in which the 1^(st)Nyquist zone included images of both carriers.

Although the present invention has been described with reference to thepreferred embodiments, it will be understood that the invention is notlimited to the details described thereof. Various substitutions andmodifications have been suggested in the foregoing description, andothers will occur to those of ordinary skill in the art. Therefore, allsuch substitutions and modifications are intended to be embraced withinthe scope of the invention as defined in the appended claims.

1. (canceled)
 2. A method for transporting communications signals, themethod comprising: receiving an analog IF signal at a first unit,wherein the analog IF signal includes a first carrier having a firstfrequency and a first bandwidth and a second carrier having a secondfrequency different from the first frequency and a second bandwidth;providing a sampling signal having a sampling frequency; converting theanalog IF signal to a digitally sampled IF signal having: the firstcarrier located in a second Nyquist zone; the second carrier located ina third Nyquist zone; an image of the first carrier located in a firstNyquist zone; and an image of the second carrier located in the firstNyquist zone; transmitting the image of the first carrier and the imageof the second carrier from the first unit to a second unit; receivingthe image of the first carrier and the image of the second carrier atthe second unit; providing a second sampling signal have a secondsampling frequency; and converting the image of the first carrier andthe image of the second carrier to the analog IF signal.
 3. The methodof claim 2 wherein the first unit comprises a DRU and the second unitcomprises a DAU.
 4. The method of claim 2 wherein the first unitcomprises a DAU and the second unit comprises a DRU.
 5. The method ofclaim 2 wherein the first Nyquist zone is centered at a frequency lowerthan a center of the second Nyquist zone, wherein the frequency of thecenter of the second Nyquist zone is lower than a center of the thirdNyquist zone.
 6. The method of claim 2 further comprising filtering thedigitally sampled IF signal.
 7. The method of claim 2 whereintransmitting the image from the first unit to a second unit isperforming using an Ethernet cable, an optical cable, a microwave link,a coaxial connection, or a wireless link.
 8. The method of claim 2wherein transmitting the image from the first unit to a second unit isvia a parallel connector independent of a SERDES.
 9. The system of claim2 wherein the first unit further comprises a filter coupled to the A/Dconverter and operable to filter out the second Nyquist zone and thethird Nyquist zone.
 10. A system for transporting communicationssignals, the system comprising: a first unit having: an input portoperable to receive an analog IF signal including a first carrier havinga first frequency and a first bandwidth and a second carrier having asecond frequency different from the first frequency and a secondbandwidth; an A/D converter coupled to the input port and operable toconvert the analog IF signal into a digitally sampled IF signal wherein:the first carrier is located in a second Nyquist zone; the secondcarrier is located in a third Nyquist zone; an image of the firstcarrier is located in a first Nyquist zone; and an image of the secondcarrier is located in the first Nyquist zone; a second unit including aD/A converter operable to convert the image of the first carrier and theimage of the second carrier into the analog IF signal; and atransmission link coupling the first unit and the second unit, whereinthe transmission link is operable to transmit the image of the firstcarrier and the image of the second carrier from the first unit to thesecond unit.
 11. The system of claim 10 wherein the first unit comprisesa DRU and the second unit comprises a DAU.
 12. The system of claim 10wherein the first unit comprises a DAU and the second unit comprises aDRU.
 13. The system of claim 10 further comprising a daisy chain ofDRUs, wherein each DRU of the daisy chain comprises an input port and anA/D converter.
 14. The system of claim 10 further comprising a daisychain of DAUs, wherein each DAU of the daisy chain comprises an inputport and an A/D converter.
 15. The system of claim 10 wherein the firstunit further comprises a filter coupled to the A/D converter andoperable to filter out the second Nyquist zone and the third Nyquistzone.
 16. The system of claim 10 wherein the transmission link comprisesan Ethernet cable, an optical cable, a microwave link, a coaxialconnection, or a wireless link.